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what you mean by joule's law

Joule's law is a physical law that defines the connection between the heat produced by the current flowing through a conductor. The law states that the heat generated by an electric current is equivalent to the product of the resistance of the conductor.

Joule’s law, in electricity, mathematical description of the rate at which resistance in a circuit converts electric energy into heat energy. The English physicist James Prescott Joule discovered in 1840 that the amount of heat per second that develops in a wire carrying a current is proportional to the electrical resistance of the wire and the square of the current. He determined that the heat evolved per second is equivalent to the electric power absorbed, or the power loss.

A quantitative form of Joule’s law is that the heat evolved per second, or the electric power loss, P, equals the current I squared times the resistance R, or P = I2R. The power P has units of watts, or joules per second, when the current is expressed in amperes and the resistance in ohms.